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Why does my truck keep eating thermostats?

post #1 of 37
Thread Starter 
My Mazda B4000/Ford Ranger keeps eating thermostats. The thermostat sticks after replacement after a week or two the engine overheats and pushes coolant out to the recovery tank. The temp gauge pegs for about 10 seconds then goes to normal. Pull the thermostat and it is stuck shut. Someone suggested that it may not be a thermostat but maybe a head gasket and when a pocket develops it damages the t'stat. I've had the vehicle in the shop to test the cooling system and it holds pressure at operating temp and cold. They also did a leak down test on all 6 cylinders with nothing conclusive. It never loses coolant other than what is pushed out to the tank. Whenever I refill the system I run the engine without the cap and there is no 'air' or bubbles coming out of the radiator. Even with a pressure tester the pressure is about 18lbs when hot. Radiator cap has been replace twice. This is very puzzling and becoming annoying. Engine is a Ford 4.0L V6. I had the engine flushed about 6 months ago and had 1 incident afterwards and change the t'stat and all was fine during the winter. then all of a sudden this has be recurring. I've gone through 4 t'stats in the last 5 or so weeks. I'm wondering if the coolant is contaminated and deposits are jamming the t'stat. Every t'stat I remove has this white substance on it. Anyone have any ideas?
post #2 of 37
There is a thermostst called the "fail-safe" it fails open if there is a problem.

Put one in your truck. It can't by design fail closed.
post #3 of 37
Have ya tried running it without the tstat, or drill a small hole in the tstat ya have? Is the pump working well? Is there any cardboard in front of the radiator from winter driving? Just some thoughts.
post #4 of 37
not being a smart arse,,,but,,,is the thermostat installed correctly? I've seen them installed up side down causing all kinds of goofy things to happen.
post #5 of 37
Just sold my ranger in Dec. Had it for 6 years and did the same thing.

When I bought it the Radiator was leaking replaced it and thats when

The heat gauge would do the same thing as yours. Had it checked and

they couldnt find any problem. Well in dec went to the store and when i came out there was coolant all over the ground . Filled up the Radiator

and drove it home . Problem ,there had been a hair crack in the head.

When the motor heated up it would seal the crack and you couldnt tell.

6 years and 72000 miles watching the heat gauge almost peg out and go back to normal and staying there .
post #6 of 37
Quote:
Originally Posted by sea jay View Post
not being a smart arse,,,but,,,is the thermostat installed correctly? I've seen them installed up side down causing all kinds of goofy things to happen.



yup- i had a company truck- toyota land cruiser- 235 straight 6

it kept overheating- couple of thermostats

turns out there was a gasket they weren't installing because it was a different part number and nobody knew to order it

happened to both our fleet mechanics and an outside guy
post #7 of 37
Thread Starter 
No cardboard but I thought about a road debris clogged AC condenser but it breaths quite well. I had it clean 2 years ago when the AC was not working properly.

The t'stat on this version of the 4.0L V6 mounts on the front of the manifold, not the top like a lot of engines that I'm used to. The way I took out the first one is the way all the others have gone in. I'm assuming the spring side goes towards the engine/manifold. I don't know that it can fit in backwards either. The goose neck is a pretty sharp turn. There is a little check valve like thing on the rim of the t'stat. I've wondered whether it should be up or down. I'm assuming up to let bubbles pass by. I've been tempted to drill a small hole in the side of the t'stat to allow some flow.

I'm really beginning to wonder if it's a matter of getting all the air out of the system. I was telling a friend that I noticed a gurgle sound in the heater yesterday morning which tells me air in the system. The t'stat is the highest point in the engine so if an air bubble is getting to the t'stat it isn't coolant that the heat sensor is getting but rather radiant heat from the engine block through the air bubble. Since I'm light on the gas and keep engine RPMs low as much as possible when driving there may not be enough flow to push air bubbles where they need to go. And if that's the case, I'm thinking that this excess heat and air bubble is damaging the t'stat.

Reading the owners manual for this truck there is a procedure for removing the air and topping off and it's repeated until the system can no longer be topped off. That's what I was not doing. I was just filling it up and putting the cap on. So I've have cycled the engine temp 6 times since yesterday and topped off the system along with a new t'stat. As it stands now, there has been no coolant loss or instability displayed by the temp gauge. The temp gauge comes up slowly rather than fast as it was doing. Keep your fingers crossed.
post #8 of 37
If your thermostat is cool enough to handle it will be closed. Many have pulled a stat, saw it was closed and figured that it was stuck.

Flush your system and use a tool called "Airlift" to refill. You most likely have either a dirty system or a bubble. Don't cheap on the coolant use OEM recomended only.
post #9 of 37
Many engines during intial warm up reqire a minimum flow thru the heater circuit ( it fows thru heater core or a bypass valve just before the core) this flow warm the thermostat and causes it to open, but without the flow the stat does not see the warm water and the engine actually overheats.
I had this problem one winter when the heater core got plugged and cut off the minimum flow.
I would remove the stat put it in boiling water on the stove and see if it is really sticking.
post #10 of 37
Thread Starter 
Did another round trip today between work and home (60 miles total) and everything was stable again. Minimal change in recovery tank level. And temp gauge seems to be the steadiest I've ever seen it since owning the truck. I think I got it. Got the fingers cross. Wish me luck.
post #11 of 37
Quote:
Originally Posted by rwalter7 View Post
No cardboard but I thought about a road debris clogged AC condenser but it breaths quite well. I had it clean 2 years ago when the AC was not working properly.

The t'stat on this version of the 4.0L V6 mounts on the front of the manifold, not the top like a lot of engines that I'm used to. The way I took out the first one is the way all the others have gone in. I'm assuming the spring side goes towards the engine/manifold. I don't know that it can fit in backwards either. The goose neck is a pretty sharp turn. There is a little check valve like thing on the rim of the t'stat. I've wondered whether it should be up or down. I'm assuming up to let bubbles pass by. I've been tempted to drill a small hole in the side of the t'stat to allow some flow.

I'm really beginning to wonder if it's a matter of getting all the air out of the system. I was telling a friend that I noticed a gurgle sound in the heater yesterday morning which tells me air in the system. The t'stat is the highest point in the engine so if an air bubble is getting to the t'stat it isn't coolant that the heat sensor is getting but rather radiant heat from the engine block through the air bubble. Since I'm light on the gas and keep engine RPMs low as much as possible when driving there may not be enough flow to push air bubbles where they need to go. And if that's the case, I'm thinking that this excess heat and air bubble is damaging the t'stat.

Reading the owners manual for this truck there is a procedure for removing the air and topping off and it's repeated until the system can no longer be topped off. That's what I was not doing. I was just filling it up and putting the cap on. So I've have cycled the engine temp 6 times since yesterday and topped off the system along with a new t'stat. As it stands now, there has been no coolant loss or instability displayed by the temp gauge. The temp gauge comes up slowly rather than fast as it was doing. Keep your fingers crossed.
I had to do my Ram on a steep hill to get the air out. I went thru the same as you and then read it on a dodge forum. It worked. If it happens again try that.
post #12 of 37
I have the same issue with my Ford Ranger. Here is what I don't understand. With a closed cooling system, why wouldn't the air bubbles get pushed out under pressure and then the recovery system fill the space up when the engine cools down, or if you just left the cap off and let the engine contnue to run why the air would not move into the radiotor where so you could just keep on topping off the system?
post #13 of 37
Quote:
Originally Posted by Churchman View Post
I had to do my Ram on a steep hill to get the air out. I went thru the same as you and then read it on a dodge forum. It worked. If it happens again try that.


I had to do the same thing to my Ram.I used a big funnel,wrapped a shop rag around the funnel where it entered the radiator and added coolant. When the T stat opened,there was a lot of bubbling as air was cleared out of the system.
post #14 of 37
Thread Starter 
Quote:
Originally Posted by 31BBert View Post
I have the same issue with my Ford Ranger. Here is what I don't understand. With a closed cooling system, why wouldn't the air bubbles get pushed out under pressure and then the recovery system fill the space up when the engine cools down, or if you just left the cap off and let the engine contnue to run why the air would not move into the radiotor where so you could just keep on topping off the system?


31BBert,
Here's my guess based on my experience with this truck. If an air bubble surrounds the t'stat, the only way it will open is from any heat conducted through the air bubble or through the heat of the engine block itself. So by the time the t'stat opens the coolant in other parts of the engine could be boiling and the system pressure will sky rocket and push coolant out to the tank. I believe the higher than normal heat was damaging the t'stat and causing it to stick. Once the t'stat opens, what remaining coolant begins to flow, engine cools down to near normal temp but because there is still a larger amount of air in the system now air bubbles are passing by the temp gauge sensor so the gauge wanders. In my case not only did the gauge wander but I could hear gurgling in the heater core when the heat was turned on. Lastly, and I'm guessing here but with that larger air volume in the cooling system insufficient vacuum is produced once the engine cools down and cannot cause a good draw on coolant in the recovery tank. This is all assuming the cooling and recovery system is air tight throughout.
post #15 of 37
Thread Starter 
Quote:
Originally Posted by bat guano View Post
I had to do the same thing to my Ram.I used a big funnel,wrapped a shop rag around the funnel where it entered the radiator and added coolant. When the T stat opened,there was a lot of bubbling as air was cleared out of the system.


I like that idea with the funnel. Good thinking. I let the coolant bubble out into a big pan which I do not like doing because some always hits the ground then I have to clean up. Royal PITA. and if you have pets you gotta be extra careful.
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